1. Field of the Invention
This invention relates to efficiency monitoring systems for power plants.
2. Discussion of Related Art
Fuel cost being a dominant factor in vessel operation has stirred interest in steam plants with multiple stages of feed heating and re-heat steam plants. It is not feasible to immediately modify the many modern steam powered merchant vessels in service by use of additional feed heater or re-heaters. Therefore, the operator must attempt to operate his existing steam powered vessels in the most efficient manner possible. The bottom line used to express a vessel's overall fuel efficiency is tons of fuel consumed per cargo ton mile. Although this figure is very useful to the owner in determining his operating costs, it contains too many variables to be used by shipyard personnel. Therefore, a less complex indication of fuel efficiency would be useful to allow the ship's crew to make adjustments in operation necessary to achieve the best heat possible efficiency.
An accurate indication of the actual fuel rate of the propulsion plant is a very useful tool for the operating engineer. During acceptance trials, the shipyard takes horsepower and fuel consumption readings and calculates an average fuel rate for certain specified conditions. These readings are averaged usually over a 15-minute period, to avoid the flucuations that usually occur. The trial rates are then normally corrected to standard conditions in accordance with SNAME recommendations.
It has been found that steam plants tend to gradually increase in fuel rate over a period of operation due to fouling of heat exchangers, wearing of pumps, and poor plant operation. Even though the operating engineer may attempt to operate the plant in an efficient manner, he cannot determine when changes or overhauls are necessary without accurate fuel rate data.
Several systems have been proposed for determining the torque, horsepower and specific fuel rate associated with a power plant. For instance, U.S. Pat. No. 3,683,684, issued Apr. 15, 1972, to Judlowe, shows a measuring apparatus which includes a vibrating wire transducer secured around the periphery of a coupling shaft. Digital circuitry is provided to generate a pulse train having a frequency proportional to the square of the vibrating wire to develop torsion information. A rotational shaft speed signal is utilized in conjunction with the output of the vibrating wire transducer to provide a signal proportional to horsepower. A fuel rate meter of the positive displacement type is employed to produce a direct measure of fuel flow. The specific fuel rate signal is computed to determine the horsepower-fuel flow quotient.
U.S. Pat. No. 3,972,224, issued Aug. 3, 1976, to Ingram, shows a shaft efficiency monitoring system which includes a husk assembly associated with the shaft and provides electrical signals proportional to shaft torque. A tachometer provides electrical signals proportional to shaft rotational speed and electrical circuitry multiplies the torque signals by the rpm signal to determine shaft horsepower. A dividing network divides the shaft horsepower signal into an electrical signal representing the rate of fuel consumption to provide a continuous indication of instantaneous system efficiency.